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Concretes Made of Magnesium–Silicate Rocks minerals Article Concretes Made of Magnesium–Silicate Rocks Lyudmila I. Khudyakova 1, Evgeniy V. Kislov 2,*, Irina Yu. Kotova 1 and Pavel L. Paleev 1 1 Baikal Institute of Nature Management, Siberian Branch, Russian Academy of Sciences, 670047 Ulan-Ude, Russia; [email protected] (L.I.K.); [email protected] (I.Y.K.); [email protected] (P.L.P.) 2 Geological Institute, Siberian Branch, Russian Academy of Sciences, 670047 Ulan-Ude, Russia * Correspondence: [email protected] Abstract: At present, there is a shortage of high-quality feedstock to produce widely used building materials—concretes. Depletion of natural resources and growing restrictions on their extraction, in connection with environmental protection, necessitate the search for an equivalent replacement for conventional raw materials. Magnesium–silicate rocks are a waste of the mining industry. We researched the possibility of using these rocks as coarse and fine aggregates in heavy concrete production. Following the requirements of the national standards, we studied the physical and mechanical characteristics of the obtained material. It was found that the strength of concrete, made of magnesium–silicate rock coarse aggregate, at the age of 28 days of hardening is within 28 MPa, while the strength of the control sample is 27.3 MPa. Replacing quartz sand with dunite sand also leads to an increase in concrete strength (~4%). Complete replacement of aggregates facilitates an increase in strength by 15–20% than the control sample. At the same time, the density of the obtained materials becomes higher. Concretes have a dense structure that affects their quality. Concrete water absorption is within 6%. The fluxing coefficient is 0.85–0.87. The application of magnesium–silicate rocks in concrete production enables the complete replacement of conventional aggregates with mining waste without reducing the quality of the obtained materials. Furthermore, the issues of environmental protection in mineral deposit development are being addressed. Citation: Khudyakova, L.I.; Kislov, E.V.; Kotova, I.Y.; Paleev, P.L. Keywords: mining waste; magnesium–silicate rocks; concretes; coarse aggregate; crushed stone; sand Concretes Made of Magnesium–Silicate Rocks. Minerals 2021, 11, 441. https://doi.org/10.3390/min11050441 1. Introduction Academic Editor: Fernando Rocha In the process of any mining, a huge number of overburden and host rocks is produced. Being in dumps negatively affects the whole environmental media [1–3]. At the present Received: 9 March 2021 stage of civilization development, it is a topical problem to involve these rocks into the Accepted: 19 April 2021 industrial turnover to produce new types of marketable products. Effective mining waste Published: 21 April 2021 management will minimize its amount and solve the problems of environmental safety at mining enterprises [4,5]. Publisher’s Note: MDPI stays neutral The main industry that uses waste from mining enterprises is construction, for which with regard to jurisdictional claims in they are high-quality raw materials. Production of concrete, consisting mainly of coarse published maps and institutional affil- and fine aggregates, is the first in this industry. iations. In the literature, there are works on using dump rocks as coarse aggregates [6,7]. At the same time, the type of crushed stone and its properties have a great influence on the quality of the obtained material [8,9]. Depending on the type of coarse aggregate, the concrete compressive strength may differ, practically, by 50% from the strength of the Copyright: © 2021 by the authors. control sample [10]. Licensee MDPI, Basel, Switzerland. River sand is conventionally used as fine aggregate. However, its shortage and This article is an open access article increasing restrictions on the extraction of natural sand in connection with environmental distributed under the terms and protection necessitate the search for alternative sources of raw materials. Rock crushing conditions of the Creative Commons Attribution (CC BY) license (https:// sand, mine refuses of crude ore can act as this alternative [11,12]. Adding them to natural creativecommons.org/licenses/by/ sand improves the physical properties of binary mixes [13]. At the same time, the quality 4.0/). Minerals 2021, 11, 441. https://doi.org/10.3390/min11050441 https://www.mdpi.com/journal/minerals Minerals 2021, 11, 441 2 of 16 of the obtained concretes depends on the shape of the particles, their surface, composition and content [14–16]. Particles of crushed rock sand have an angular shape and smooth surface. Concretes containing the optimal amount of this aggregate have higher water demand, a smaller air volume, higher density and strength [17]. According to physical and mechanical characteristics, silicate rocks, formed as a result of phosphate raw material extraction, are suitable for producing concrete B25 (25 MPa). The tests showed that materials made of them have high strength, and their quality is not inferior to the control sample [7]. Studies on using granite extraction and processing waste (granite sludge) showed that it could be used to produce self-compacting mortar. If the granite sludge is up to 40% of the aggregate mass, the physical and mechanical characteristics of the mortar correspond with the control sample [18]. During coal mining, there is a huge amount of waste produced, consisting mainly of aleurolites and sandstones. After preparatory works, they can be used as a substitute for natural sand in concrete production. To obtain materials of good quality, the amount of waste should not exceed 50% of the fine aggregate mass [19]. Keramzite from coal processing waste is the raw material for light concrete production. The frangibility of keramzite concrete coarse aggregate from carbon-veil rocks is stabilized by 28 days of hardening. The compressive strength of the obtained material is 39–42 MPa and corresponds with the strength of the control sample [20]. Fluorite sand waste is an alternative to natural sand. Replacing this with up to 70% of the conventional aggregate, it is possible to obtain concretes with high elastic modulus, tensile and compressive strength [21]. When using mine refuse as fine aggregate, it is necessary to consider that adding it into the concrete composition reduces its placeability. It is shown in [22] that the maximum content of mine refuses for the beneficiation of lead-zinc and copper ores in concrete should not exceed 30% of the fine aggregate mass since a higher percentage leads to a decrease in the strength characteristics of the obtained material. However, when using iron ore mine refuses, the optimal replacement percentage of natural sand varies within different limits. In the research [23], it is 20%, and in the research [24] is 35%. A further increase in the waste content deteriorates the physical and mechanical characteristics of concretes. For road construction, concrete mixes can contain up to 40% of iron ore mine refuses (complete sand replacement). At the same time, slag cement activated by alkalis is used as bonding material [25]. Copper mine refuses to have an increased content of fine fraction. Therefore, their content should not exceed 15% of the concrete composition. The obtained materials are suitable for paving stone and block production [26]. Among the mining waste, there is a great number of magnesium–silicate rocks. They are part of ultramafic–mafic massifs distributed throughout the world. They include mineral deposits of various types: Ni-Cu and PGE [27], Cr [28], Fe- Ti-V [29], asbestos [30], jadeite and nephrite [31], magnesite, talc, vermiculite [32] et al. Kimberlite and lamproite pipes contain diamonds [33,34]. In their natural state, the com- plexes do not have a significant impact on the environment. However, they become a source of negative impact on nature in the process of mining. All these deposits contain a small proportion of valuable components. This is especially true for diamond and metal ore deposits. More than 90% of the extracted rock mass goes to dumps, taking into account dilution during mining. Minerals 2021, 11, 441 3 of 16 While there are huge reserves, magnesium–silicate rocks are practically not used, although they are of good quality. Therefore, their application in the production of com- mercial products is an actual task. Let us examine the possibility of their application in the production of heavy concretes. The solution to using magnesium–silicate rocks is shown by the example of the Yoko– Dovyren dunite–troctolite–gabbro stratified massif, Northern Baikal region, Russia [35,36]. The Yoko–Dovyren intrusive is located in the southern folded margin of the Siberian craton, 60 km to the northeast of Lake Baikal. It lies subconcordantly in carbonate- terrigenous rocks (mainly black shale) of the Synnyr rift [37–39]. The Yoko–Dovyren massif is 26.0 × 3.5 km2 in size. It is part of the Synnyr–Dovyren volcanic-plutonic complex. The complex also includes underlying sills of plagioperidotites and dikes of gabbronorites [38,40] with similar dikes in the roof. The complex includes effusives of the Synnyr ridge, overlapping these bodies, highly titanian basalts of the Inyapuk suite, low-titanian andesites and basalts of the Synnyr suite [41]. The geochemical and isotope data indicate a genetic relationship between intrusive and low-titanian volcanic rocks [42]. U-Pb ages of zircons are 728.4 ± 3.4 Ma for the Yoko–Dovyren massif and 722 ± 7 Ma for the associating volcanites [43,44]. Using baddeleyite from pegmatoid gabbronorites in the roof, U-Pb dating gave 724.7 ± 2.5 Ma [45]. As a result of tectonic movements, the Yoko–Dovyren massif has an almost vertical position. The intrusive is composed of contact rocks (chilled gabbronorites and picrodolerites, further plagioclase lherzolites), there are five zones above them (bottom-up): dunite (Ol + Chr) ! troctolite + plagiodunite (Ol + Pl. + Chr) ! troctolite + olivine gabbro (Ol + Pl + Chr ± Cpx) ! olivine gabbro (Pl + Ol + Cpx ± Chr) ! olivine gabbronorite (Pl + Ol + Cpx ± Opx).
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